Following an increase in speed of signal, the differential transmission system is widely adopted. Although the differential transmission system is advantageous for noise reduction, as the signal becomes faster, signal degradation to be caused due to generation of a common-mode noise has become problematic.
Now, in an insulating layer of the multilayered transmission line plate, in order to secure handling properties of materials at the time of manufacture of multilayered transmission line plate, mechanical properties of the multilayered transmission line plate itself, and so on, a composite material of a glass cloth and a resin is widely used.
As shown in FIG. 1, the glass cloth 101 has a structure in which glass fibers (warp) 102 and glass fibers (weft) 103 are woven vertically and horizontally, respectively, and therefore, the glass fibers overlap in a weave texture portion. Accordingly, in the composite material of a glass cloth and a resin, the abundance ratio of glass becomes high in the weave texture portion of glass fibers. Conversely, the abundance ratio of glass becomes low in a portion where the glass fibers do not overlap. In general, since the resin and the glass are different from each other in a dielectric constant, when the abundance ratio between the resin and the glass within the composite material plane is heterogeneous, the dielectric constant within the composite material plane becomes heterogeneous, too.
As shown in FIG. 2, in a multilayered transmission line plate in which a differential wiring 206 is formed between ground layers 210, 205, there is caused a case where a wiring is present in a portion 202 where the abundance ratio of glass 204 is high and a portion 203 where the abundance ratio of glass 204 is low. However, since the signal speed is different in the respective places, a deviation (skew) in arrival time of signal is generated at the receiving side, resulting in lowering of signal quality.
As a skew countermeasure, a measure by a design technology, such as oblique disposition of a wiring pattern against the weaving direction of glass, etc., is taken. However, according to this method, imposition of the wiring pattern becomes inefficient, resulting in a material loss. Thus, another solution means is required.
PTL 1 discloses a method of concentratedly adding fillers with a high dielectric constant in portions of a glass cloth that are not a weave texture, thereby making the dielectric constant within the composite material plane homogeneous.